1. Field of the Invention
This invention concerns an oil recovery process and more specifically a surfactant-containing emulsion flooding oil recovery process. Still more specifically, this invention is concerned with an oil recovery process using a water-external phase emulsion comprising a dispersed hydrocarbon phase and a continuous aqueous phase, the emulsion containing a water soluble alkylpolyalkoxyalkylene sulfonate or alkylarylpolyalkoxyalkylene sulfonate anionic surfactant and a low HLB nonionic surfactant, which emulsion is phase stable and suitable for flooding formations containing high concentrations of salt and/or divalent ions such as calcium and magnesium, in formations whose temperatures are in the range of from about 70.degree. to about 300.degree. F.
2. Description of the Prior Art
Petroleum is recovered from subterranean formations in which it has accumulated, by penetrating the formation with one or more wells and pumping or permitting the petroleum to flow to the surface through these wells. Recovery of petroleum from formations is possible only if certain conditions exist in the formations. The petroleum must be present in the formation in an adequately high concentration, and there must be sufficient permeability or interconnected flow channels within the formation to permit the flow of fluids therethrough if sufficient pressure is applied to the fluid. When the formation has natural energy present in the form of an active, underlying or edge water drive, or gas dissolved in the petroleum to the producing well, or a high pressure gas cap above the petroleum-saturated portion of the formation, this natural energy is utilized first to recover petroleum. Recovery of petroleum in this manner using natural energy is referred to in the art as primary recovery. When this natural energy source is depleted, or in the instance of those formations which do not contain sufficient natural energy initially to support primary recovery, some form of supplemental or enhanced recovery process must be applied to the formation in order to extract petroleum therefrom. Supplemental recovery is sometimes referred to as tertiary recovery, although in fact it may be primary, secondary or tertiary in sequence of employment.
Waterflooding, which involves the injection of water into the subterranean, petroleum-containing formation for the purpose of displacing petroleum toward the producing well, is the most economical and widely practiced supplemental recovery method. Water does not displace the petroleum efficiently, however, due to at least in part to the fact that water and oil are immiscible and the interfacial tension between water and oil is quite high. Persons skilled in the art of oil recovery have recognized this limitation of waterflooding and many additives have been described in the literature for incorporation in the flooding water to reduce the interfacial tension between the injected water and the formation petroleum. U.S. Pat. No. 2,233,381 (1941) discloses the use of polyglycol ethers as surface acitve agents or surfactants too increase the capillary displacement efficiency of an aqueous flooding medium. U.S. Pat. No. 3,302,713 discloses the use of petroleum sulfonates prepared from specified boiling range fractions of petroleum feedstock as a surfactant in surfactant flooding supplemental oil recovery operations. Other surfactants which have been proposed for oil recovery operations include alkylpyridinium salts, alkyl sulfates, alkylaryl sulfates, ethoxylated alkyl or alkylaryl sulfates, alkyl sulfonates, alkyaryl sulfonates, and quarternary ammonium salts.
The above described surfactants are satisfactory in certain limited applications, particularly in formations containing water whose salinity and hardness, i.e. concentration of divalent ions including calcium and magnesium, and/or temperature, are relatively low. For example, when the salinity of the formation water is less than about 30,000 parts per million and the concentration of divalent ions is less than about 200 to 500 parts per million, petroleum sulfonates are very effective over a broad temperature range. U.S. Pat. Nos. 3,792,731; 3,811,504; 3,811,505; and 3,811,507 describe oil recovery processes employing specified mixtures of water soluble anionic and water soluble nonionic surfactants which exhibit satisfactory performance in petroleum formations containing water having high concentrations of divalent ions, i.e. in the concentration range of from about 500 to 18,000 parts per million calcium and magnesium, but cannot be used in formations whose temperature exceed about 150.degree. F. because of the cloud point limitations of nonionic surfactants.
U.S. Pat. No. 3,508,612 describes an oil recovery method using an aliphatic polyethoxy sulfate and an organic sulfonate. U.S. Pat. No. 3,888,308 describes the use of an aqueous solution of an alkyl or alkylpolyethoxy sulfate as a mobility buffer. U.S. Pat. Nos. 3,827,497 and 3,890,239 describe an oil recovery process and a fluid containing an organic sulfonate and an alkylpolyethoxy sulfonate. U.S. Pat. No. 3,977,471 describes an oil recovery process and a substantially oil-free fluid, e.g. a solution, employing an alkylarylpolyalkoxyalkyl sulfonate in single surfactant mode.
Oil recovery processes employing a substantially oil-free aqueous fluid containing an alkylpolyethoxyalkyl sulfonate or alkylarylpolyalkoxyalkyl sulfonate are uniquely suitable for use in high temperature, high salinity reservoirs. A low HLB, essentially water insoluble nonionic surfactant such as a polyethoxylated alkanol or polyethoxylated alkylphenol may be used in combination with the alkyl or alkylarylpolyalkoxyalkyl sulfonate to ensure phase stability of the aqueous fluid.
It is desirable that the viscosity of the oil recovery fluid be at least slightly greater than water and preferably greater than the crude oil present in the formation to ensure effective volumetric displacement. Microemulsions, emulsions and micellar dispersions exhibit greater viscosities than true solutions of surfactant but it is difficult to form an emulsion which is stable at high temperatures and in the presence of high salinity. Hydrophylic polymers may be incorporated in surfactant solutions to increase their viscosity, but most polymers are not stable at high temperatures or salinities and an interaction occurs between hydrophylic polymers and many surfactants.
In view of the foregoing discussion, it can be appreciated that there is a substantial, unfulfilled commercial need for a surfactant oil recovery method using a phase stable emulsion, microemulsion or micellar dispersion, preferably a viscous emulsion which can be injected into formations whose temperatures are in excess of 70.degree. F., up to 300.degree. F. which formations also contain water having salinities higher than about 30,000 parts per million total dissolved solids, and/or concentrations of divalent ions greater than about 2,000 parts per million.